Over the last four decades, reducing the weight of aircrafts has been the main priority to solve the cost equation between energy consumption and optimal performances. The aircraft structures have been highly lightened thanks to composite materials, especially thermosetting (TS) polymer matrices which have been widely used. However the engine mass in an aircraft still remains significant and its decrease is challenging principally due to the severe thermal environment. Thus, in order to increase the temperature-limit use of organic composites for the engine applications, one can propose (i) to increase the glass transition temperature of TS or amorphous thermoplastic matrices or (ii) to use semi-crystalline thermoplastics (TP) matrices in their rubber-like state.
In accordance with helicopter-engine specifications, the present work deals with the characterization of the mechanical behavior of UD carbon PEEK laminates for different temperatures from glassy domain to rubber-like state. Neat PEEK resin exhibits a glass transition temperature equal to 143°C and a melting temperature of 343°C. Several panels have been manufactured using thermo-compression and hand lay-up with different stacking sequences: n, [0,90]nS and [+45,-45]nS and based on continuous carbon fiber reinforced PEEK prepreg laminate supplied by Tencate. A wide campaign of tensile tests is achieved at different temperatures up to 200°C. They are conducted on each staking sequence in order to measure the mechanical properties as function of temperature. Following the fracture surface is analyzed by SEM observations. Moreover the material is tested in flexion loading from the room temperature to the melting temperature of PEEK. In order to analyze the time-dependent behavior across the glass transition, creep tests are achieved at 100 and 200°C. In parallel the linear rheological behavior is measured on the neat resin and the composites. In addition the structure/property relationship is deeply examined as regards the fiber/matrix interface. Based on the experimental results, an appropriate numerical model will be developed to describe the constitutive laws (thermo-visco-elasticity) of the material in its rubber-like state.
The main goal of the present work is to observe, explain and model the evolution of the thermo-mechanical behavior of the composite material across the glass transition of its PEEK matrix.